The present invention relates to an improved uranium peroxide and processes for preparing same from uraniferous solutions, and more particularly, it relates to uranium peroxide in the form of substantially spherical particles with well-defined particle size having an increased apparent bulk density and a very good flowability, as well as to a process for obtaining such uranium peroxides by crystallization and agglomeration starting from uraniferous solutions.
Uranium peroxide is a uraniferous concentrate which can be used in plants for the conversion of uraniferous concentrates to uranium fluoride or uranium oxide, which are useful for the preparation of nuclear fuels. Their great advantage with respect to prior art concentrates such as sodium uranate is that they do not contain sodium ions. Such sodium ions are in effect increasingly proscribed in plants for refining uranium-containing concentrates.
The production of uranium-bearing concentrates not containing sodium has generally become necessary in recent years. The conversion of uranium-containing concentrates containing sodium uranate, products actually from a certain number of treatment facilities for uranium minerals, to uranium peroxide is a means of eliminating the sodium ions. After dissolution of the sodium uranate in sulfuric acid, the uranium-containing solution so obtained can be treated with hydrogen peroxide to precipitate the uranium peroxide.
According to the prior art extraction technique described for example by R. Merrit in The Extraction Metallurgy of Uranium, Library of Congress Catalog, pages 240-246, the uranium contained in uranium-bearing minerals is recovered, after chemical attack of the minerals, and purification and concentration of the resulting uranium-bearing solution, in the form of acid liquors, for example, in a medium of sulfate ions. The uranium-containing concentrate can be obtained, starting from these solutions, by precipitation with the use of hydrogen peroxide, in the form of uranium peroxide. This is a well-known operation which is so described in U.S. Pat. No. 2,770,521, and it is used commercially only with relatively concentrated solutions resulting from the elution of uranium on a resin or from solvent extraction of the uranium, that is to say, from solutions containing at least about 10 g/L of uranium.
Upon treatment of the uranium-bearing solutions by hydrogen peroxide according to the prior art process, the precipitation takes place in agitated vessels disposed in series. The pH is maintained between 2.5 and 4 and the temperature is maintained between 30.degree. and 65.degree. C. The uranium peroxide precipitate so obtained is very fine and difficult to filter and to dry. The particles have a size of between 0 and 10 .mu.m, with an irregular shape which leads to bad flowability. The handling of such products creates health problems and security problems because of the emission of uranium-rich dusts, both in plants for producing uranium-bearing concentrates, at the time of drying and of placing the material in solid casks, and in refining plants which recover these uranium-bearing concentrates to purify them and convert them into oxide, fluoride, and metal.
There accordingly exists a considerable commercial need for a treatment process for uranium-bearing solutions leading to a uranium-bearing concentrate in the form of uranium peroxide which does not contain sodium ions and which exhibits a great ease of filtration and a great security of handling without the emission of uranium-rich dusts.